1. Field of the Invention
Aspects of the present invention relate to a printer of an inkjet system for performing image recording by discharging ink drops on a recording medium and, more specifically, to a system for supplying ink from an ink tank.
2. Description of the Related Art
In the related art, a color printer is known in which a color image is recorded onto on a printing medium using inks of different color hues such as cyan (C), magenta (M), yellow (Y), and black (Bk). Although various printing systems are employed in color printing, so called “inkjet systems” are in general use (in which images are recoded on a printing medium by pressurizing and injecting ink through the use of partial deformation of a nozzle hole on a recording head or local ink boiling). In a color printer employing the inkjet system, the various colors of ink are supplied from ink tanks in which the respective colors of ink are supplied to a recording head, and the recording head selectively discharges the ink in the respective colors from nozzles according to a predetermined system, so that minute dots are formed on the recording medium. Accordingly, a desired color image is formed on the recording medium.
In the color printer of this type, positions for mounting the ink tanks for the respective colors are generally fixed in advance. On the other hand, one known system describes an inkjet recording apparatus in which an ink tank of another color, such as an ink tank for black (Bk) (black ink tank), may be mounted to positions where ink tanks for cyan (C), magenta (M), and yellow (Y) are mounted, so that recording control according to the ink color in the ink tank is performed. This inkjet recording apparatus functions as a color printer when the ink tanks for the respective colors (color ink tanks) are mounted. When all the color ink tanks are replaced with the black ink tanks, the recording apparatus functions as a monochrome specific printer. In this case, black ink is discharged from all the nozzles on the recording head so that high-speed monochrome printing is enabled. When the black ink tanks are replaced with the original color ink tanks, the recording apparatus may be used as the color printer.
In the printer of an inkjet system, when the ink tank is replaced with a new ink tank, a purging process is performed for sucking and removing residual ink from the recording head as well as air bubbles from the nozzles of the recording head. The purging process is of course performed in the case in which the ink tanks are replaced in the inkjet recording apparatus. However, in these inkjet printing systems, when an ink tank of a different color is mounted in the position previously occupied by an ink tank of another color, residual ink in an ink needle or a push rod is interfused into the ink tank and is dispersed therein. Hence, the ink of the old color is disadvantageously mixed with the new ink of the new color after replacement. Assuming that the residual ink is not dispersed in the entire area in the ink tank, part of the ink mixed in the ink tank cannot be sucked and removed sufficiently with the normal purging process even when the purging process is carried out after the replacement of the ink tank. On the other hand, although it is assumed that the mixed ink is sucked and removed when the purging process is carried out for a long time, a large amount of ink is undesirably used in the purging process and hence wasted.
When an ink tank of a different color (from the color of another color previously located at a given position) is mounted to the given position, the ink after replacement is mixed with the residual ink remaining in a flow path in the recording head and hence a mixed color is generated. In this case, it is necessary to remove the mixed color ink by the purging process. However, the time required for removing the mixed color ink by the purging process differs depending on the difference between the ink color used before the replacement of the ink tank and the ink color used after the replacement. For example, when the ink is changed from a light color (yellow, for example) to a dark color (black), since the light color of the ink is absorbed by the ink in the dark color, a purging process lasting only a short time will be sufficient for removing the mixed color ink. In contrast, when the ink is changed from the dark color (black) to the light color (yellow), the light color ink may be changed in color by the ink in the dark color by mixing, so that the system is required to suck and remove a large amount of the former ink. Hence the purging process needs to be carried out for a long time. If the same purging process is carried out under such a circumstance as well, not only an excess of ink is disposed, but also it takes a long time to achieve a printable state.